I work in the Event Horizon Telescope, studying jets accelerated by black holes, and immediate black hole surroundings as well. I do ray tracing / radiative transfer simulations, and this app is an adaptation of those simulations – with the primary focus on being physically accurate under reasonable assumptions.
And totally, I enjoyed listening to Kip Thorne's lectures and talking to him, he gives them in a very approachable style while remaining honest!
Forgot to answer this first!
Basically, ~1 cm radius black hole has the mass of the Earth – really, Earth would need to get this small to become a black hole. I've made a very simple demo for a kids lecture I gave recently, https://plav.in/outreach_demos/squeeze-earth-v2.html. Also see https://xkcd.com/1680/ of course :)